Donald Trump’s critics say the only way for him to keep his business interests separate from the public’s interest is to simply get out of business entirely, selling his companies and putting the proceeds into anonymous assets that someone else can manage.But there’s nothing simple about it: unloading a real estate empire as large as Trump’s is a lengthy, complicated process fraught with ethical pitfalls, one that could end up costing a fortune.“He has to make a choice,” said David Reiss, director of Brooklyn Law’s Center for Urban Business Entrepreneurship.